Projection-type display device

ABSTRACT

A projection-type display device which is used in a projector device for projecting optical images spatially modulated by reflection-type liquid crystal panels onto a screen to display an image, wherein a wavelength separation mirror is arranged so that an angle exhibited by an optical axis of light incident on the wavelength separation mirror and the optical axis of reflected light becomes smaller than 90 degrees or polarization filters or polarization separation elements are arranged on an incident facet side or an emission facet side of optical separation elements.

This application is a continuation of U.S. patent application Ser. No.09/404,020 filed on Sep. 23, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection-type display device whichcan be applied to for example a projector device for projecting anoptical image spatially modulated by a reflection-type liquid crystalpanel onto a screen.

2. Description of the Related Art

In the related art, a projection-type display device has been proposedwhich is configured to use a reflection-type liquid crystal panel togenerate a spatially modulated optical image and to project this opticalimage onto the screen so as to form a desired color image.

FIG. 1 is a view of the configuration of this type of projection-typedisplay device.

In this projection-type display device 1, a light source 2 isconstituted by for example a discharge lamp 3 and a reflector 4 andemits white illumination light. A convex lens 5 converts theillumination light emitted from the light source 2 to a substantiallyparallel luminous flux and then emits it.

A color separation mirror 6 on the optical path of the illuminationlight emitted from this convex lens 5 reflects the illumination lighthaving a predetermined wavelength and transmits the remainingillumination light therethrough. A color separation mirror 7 on theoptical path of the illumination light reflected at this colorseparation mirror 6 reflects the illumination light having apredetermined wavelength and transmits the remaining illumination lighttherethrough. Due to this, the projection-type display device 1separates the illumination light emitted from the light source 2 to red,blue, and green illumination light.

A lens 8, a mirror 9, and a lens 10 bend the optical path of theillumination light transmitted through the color separation mirror 6 toguide the light to a polarization beam splitter 11. The polarizationbeam splitter 11 emits illumination light having a predetermined planepolarization in the illumination light striking from this lens 10 towarda reflection-type liquid crystal panel 12 and transmits the illuminationlight having a plane polarization orthogonal to this plane polarization.Further, the polarization beam splitter 11 transmits a predeterminedpolarization component in the optical image emitted after spatiallymodulating the illumination light at the reflection-type liquid crystalpanel 12 and emits it to a color synthesizing prism 13.

A polarization beam splitter 14 similarly emits the illumination lighthaving a predetermined plane polarization in the illumination lightreflected at the color separation mirror 7 toward the reflection-typeliquid crystal panel 15 and transmits the illumination light having theplane polarization orthogonal to this plane polarization therethrough.Further, the polarization beam splitter 14 transmits a predeterminedpolarization component in the optical image emitted after spatiallymodulation of the illumination light at the reflection-type liquidcrystal panel 15 therethrough and emits it to the color synthesizingprism 13.

A polarization beam splitter 16 similarly emits the illumination lighthaving a predetermined plane polarization in the illumination lightreflected at the color separation mirror 7 toward the reflection-typeliquid crystal panel 17 and transmits the illumination light having aplane polarization orthogonal to this plane polarization therethrough.Further, the polarization beam splitter 16 transmits a predeterminedpolarization component in the optical image emitted after spatiallymodulation of the illumination light at the reflection-type liquidcrystal panel 17 therethrough and emits it to the color synthesizingprism 13.

The reflection-type liquid crystal panels 12, 15, and 17 spatiallymodulate the illumination light according to color signals correspondingto the wavelengths of the incident illumination light by being driven bya not illustrated drive circuit and project optical images rotated intheir plane polarizations with respect to the illumination light towardthe polarization beam splitters 11, 14, and 16.

The color synthesizing prism 13 combines the optical images incidentfrom these polarization beam splitters 11, 14, and 16 and emits theresult. A projection lens 19 projects the resultant optical imageemitted from this color synthesizing prism 13 onto the screen 20.

Due to this, the projection-type display device 1 enlarges and projectsthe images formed on the reflection-type liquid crystal panels 12, 15,and 17 onto the screen 20 to thus display the intended color image.

The polarization beam splitters 11, 14, and 16 used for this type ofprojection-type display device 1, however, also reflect and emit severalpercent of the amount of light incident of the components of planepolarization which originally must be transmitted. In theprojection-type display device 1, therefore, the unrequired planepolarization components reflected at the polarization beam splitters 11,14, and 16 in this way are returned from the reflection-type liquidcrystal panels 12, 15, and 17 to the polarization beam splitters 11, 14,and 16 and projected onto the screen 20 via the color synthesizing prism13.

Further, unmodulated components which are never polarized, but arereflected are also contained also in the modulated light reflected atthe reflection-type liquid crystal panels 12, 15, and 17. In theprojection-type display device 1, such components are also projectedonto the screen 20 via the color synthesizing prism 13.

Due to this, the projection-type display device 1 suffers from thedefect of the haze phenomenon where a portion which should be originallydisplayed black is displayed white, so there is a problem that thecontrast of the display image is still insufficient by that amount inpractical use and the quality of the display image is poor.

Below, this haze phenomenon will be further considered from theviewpoint of the structure of the polarization beam splitter.

When a black portion is displayed white and this haze phenomenon ismanifested, the contrast cannot be sufficiently secured by that amountin the image displayed on the screen.

A polarization beam splitter is formed by adhering inclined facets ofrectangular prisms to each other. The incident light is detected by alaminate of dielectric films at the inclined facets. Accordingly, in thetransmitted light and the reflected light of the polarization beamsplitter, originally the linear polarized light resulting from thisdetection must be emitted.

The glass material constituting this type of rectangular prism, however,has a birefringence property. Due to this, the reflected light and thetransmitted light to be originally emitted by the linear polarizationare emitted by elliptical polarization.

Namely, the reflected light and the transmitted light comes to containlight having a plane polarization orthogonal to the plane polarizationoriginally aimed at. Further, the light incident due to linearpolarization comes to be detected by elliptical polarization, thereforepart of the light to be originally transmitted or reflected will bereflected or transmitted by that amount and emitted reverse to theformer.

When viewing this from the standpoint of the optical images emittedtoward the polarization beam splitters from the reflection-type liquidcrystal panels, the reflection-type liquid crystal panels spatiallymodulate the incident light having the predetermined plane polarizationsand reflect optical images as the synthesized light of p-polarizationcomponents and s-polarization components. The optical images emitted inthis way originally must be separated into the p-polarization componentsand the s-polarization components by the polarization beam splitters andonly the optical images of the p-polarization components projected ontothe screen.

However, the optical images become elliptical polarized light due to thebirefringence of the polarization beam splitters. As a result, part ofthe s-polarization components subjected to no spatial modulation will beprojected onto the screen.

Further, when viewing the illumination light emitted from thepolarization beam splitters toward the reflection-type liquid crystalpanels, the components of the plane polarization orthogonal to theillumination light having the predetermined plane polarization to bespatially modulated at the reflection-type liquid crystal panels willleak in. This leaked illumination light will be projected onto thescreen as it is.

Note that, if the above haze phenomenon nonuniformly occurs, the imagedisplayed in the projection-type display device 1 will deteriorate inuniformity.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a projection-typedisplay device capable of displaying a high quality display image byimproving the contrast.

According to a first aspect of the present invention, there is provideda projection-type display device, comprising at least a firstreflection-type image-forming means for spatially modulating andreflecting an incident first illumination light to emit a first opticalimage, a second reflection-type image-forming means for spatiallymodulating and reflecting an incident second illumination light to emita second optical image, a wavelength separation mirror for reflectingillumination light of a predetermined wavelength in incident light andemitting it as the first illumination light to the first reflection-typeimage-forming means and transmitting the remaining illumination lightand emitting it as the second illumination light to the secondreflection-type image-forming means so as to reflect the first opticalimage and transmit the second optical image and emit the first andsecond optical images so as to follow the optical path of the incidentlight in reverse, a projection optical system for projecting the firstand second optical images, a light source for emitting predeterminedlight to the wavelength separation mirror as the incident light, and alight separating means for emitting the incident light emitted from thelight source to the wavelength separation mirror and emitting the firstand second optical images incident from the wavelength separation mirrorto the projection optical image, the inclination of the wavelengthseparation mirror set so that the optical axis of the light incident onthe wavelength separation mirror and the optical axis of the firstoptical image becomes smaller than 90 degrees.

According to a second aspect of the present invention, there is provideda projection-type display device, comprising at least a firstreflection-type image-forming means for spatially modulating andreflecting an incident first illumination light to emit a first opticalimage, a second reflection-type image-forming means for spatiallymodulating and reflecting an incident second illumination light to emita second optical image, a third reflection-type image-forming means forspatially modulating and reflecting an incident third illumination lightto emit a third optical image, a first wavelength separation mirror forreflecting illumination light of a predetermined wavelength in incidentlight and emitting it as the first illumination light to the firstreflection-type image-forming means and transmitting and emitting theremaining illumination light so as to reflect the first optical imageand transmit the second and third optical images and emit the first,second, and third optical images so as to follow the optical path of theincident light in reverse, a second wavelength separation mirror forreflecting illumination light of a predetermined wavelength in lighttransmitted through the first wavelength separation mirror and emittingit as the second illumination light to the second reflection-typeimage-forming means and transmitting the remaining illumination lightand emitting it as the third illumination light to the thirdreflection-type image-forming means so as to reflect the second opticalimage and transmit the third optical image and emit the second and thirdoptical images toward the first wavelength separation mirror, aprojection optical system for projecting the first, second, and thirdoptical images, a light source for emitting predetermined light to thefirst wavelength separation mirror as the incident light, and a lightseparating means for emitting the incident light emitted from the lightsource to the first wavelength separation mirror and emitting the first,second, and third optical images incident from the first wavelengthseparation mirror to the projection optical image, the inclination ofthe first wavelength separation mirror set so that the optical axis ofthe light incident on the first wavelength separation mirror and theoptical axis of the first optical image becomes smaller than 90 degrees,the inclination of the second wavelength separation mirror set so thatthe optical axis of the light incident on the second wavelengthseparation mirror and passing through the first wavelength separationmirror and the optical axis of the second optical image becomes smallerthan 90 degrees.

Preferably, the first reflection-type image-forming means emits thefirst optical image with a plane polarization rotated with respect tothe incident light and a polarization filter for selectivelytransmitting illumination light of a plane polarization corresponding tothe plane polarization of the light incident on the firstreflection-type image-forming means is arranged between the light sourceand the light separating means.

Alternatively, preferably, the first reflection-type image-forming meansemits the first optical image with a plane polarization rotated withrespect to the incident light and a polarization filter for selectivelytransmitting incident light of a plane polarization corresponding to theplane polarization of the first optical image is arranged between theprojection optical system and the light separating means.

Alternatively, preferably, the first reflection-type image-forming meansemits the first optical image with a plane polarization rotated withrespect to the incident light, a first polarization filter forselectively transmitting illumination light of a plane polarizationcorresponding to the plane polarization of the light incident on thefirst reflection-type image-forming means is arranged between the lightsource and the light separating means, and a second polarization filterfor selectively transmitting incident light of a plane polarizationcorresponding to the plane polarization of the first optical image isarranged between the projection optical system and the light separatingmeans.

According to a third aspect of the present invention, there is provideda projection-type display device, comprising a reflection-typeimage-forming means for spatially modulating and reflecting illuminationlight of a predetermined plane polarization to emit an optical imagewith a plane polarization rotated with respect to the plane polarizationof the illumination light, a projection optical system for projectingthe optical image, a light source for emitting the illumination light,and a light separating means for emitting the illumination light emittedfrom the light source toward the reflection-type image-forming means andemitting the optical image emitted from the reflection-typeimage-forming means to the projection optical system, a polarizationseparation element for selectively transmitting illumination light of aplane polarization corresponding to the plane polarization of the lightincident on the reflection-type image-forming means and selectivelyreflecting the component of the plane polarization orthogonal to thatplane polarization arranged between the light source and the lightseparating means.

Preferably, the polarization separation element is formed on an incidentfacet of the illumination light of the light separating means.

According to a fourth aspect of the present invention, there is provideda projection-type display device provided with a reflection-typeimage-forming means for spatially modulating and reflecting illuminationlight of a predetermined plane polarization to emit an optical imagewith a plane polarization rotated with respect to the plane polarizationof the illumination light, a projection optical system for projectingthe optical image, a light source for emitting the illumination light,and a light separating means for emitting the illumination light emittedfrom the light source toward the reflection-type image-forming means andemitting the optical image emitted from the reflection-typeimage-forming means to the projection optical system, a polarizationseparation element for selectively transmitting incident light of apredetermined plane polarization corresponding to the plane polarizationof the optical image and selectively reflecting the component of theplane polarization orthogonal to that plane polarization arrangedbetween the projection optical system and the light separating means.

Preferably, the polarization separation element is formed on an emissionfacet of the optical image of the light separating means.

According to a fifth aspect of the present invention, there is provideda projection-type display device provided with a reflection-typeimage-forming means for spatially modulating and reflecting illuminationlight of a predetermined plane polarization to emit an optical imagewith a plane polarization rotated with respect to the plane polarizationof the illumination light, a projection optical system for projectingthe optical image, a light source for emitting the illumination light,and a light separating means for emitting the illumination light emittedfrom the light source toward the reflection-type image-forming means andemitting the optical image emitted from the reflection-typeimage-forming means to the projection optical system, a firstpolarization separation element for selectively transmittingillumination light of a plane polarization corresponding to the planepolarization of the light incident on the reflection-type image-formingmeans and selectively reflecting the component of the plane polarizationorthogonal to that plane polarization arranged between the light sourceand the light separating means, a second polarization separation elementfor selectively transmitting incident light of a predetermined planepolarization corresponding to the plane polarization of the opticalimage and selectively reflecting the component of the plane polarizationorthogonal to that plane polarization arranged between the projectionoptical system and the light separating means.

Preferably, the first polarization separation element is formed on anincident facet of the illumination light of the light separating means.

Alternatively, preferably the second polarization separation element isformed on an emission facet of the optical image of the light separatingmeans.

According to a sixth aspect of the present invention, there is provideda projection-type display device provided with a reflection-typeimage-forming means for spatially modulating illumination light of apredetermined plane polarization to emit an optical image with a planepolarization rotated with respect to the plane polarization of theillumination light, a projection optical system for projecting theoptical image, a light source for emitting the illumination light, and apolarization beam splitter for emitting the illumination light emittedfrom the light source toward the reflection-type image-forming means andemitting a predetermined polarization component in the optical lightincident from the reflection-type image-forming means to the projectionoptical system, the polarization beam splitter being formed by a membersatisfying the following relationship:${5.00 \times 10^{2}} \geq {{K \cdot \alpha \cdot E \cdot \frac{Cp}{\rho}}{\int_{\lambda_{2}}^{\lambda_{1}}{\left( {1 - T} \right){\lambda}}}}$

where, K: photoelasticity constant of the member (nm/mm·mm²/N),

α: linear expansion coefficient of the member (10⁻⁶/K),

E: Young's modulus of the member (10³N/mm²),

λ: wavelength of the illumination light (nm),

T: internal transmittance of the member at the wavelength λ,

ρ: specific gravity of the member (g/cm³), and

Cp: specific heat of the member (J/g·k),

the integration range in Equation being a range of the light absorptionwavelength band of the member.

According to a seventh aspect of the present invention, there isprovided a projection-type display device provided with a plurality ofreflection-type image-forming means each of which for spatiallymodulating incident light of a predetermined wavelength and emitting anoptical image with a plane polarization rotated with respect to theplane polarization of the incident light, a light source for emittingillumination light, a dichroic prism for emitting illumination lightemitted from the light source to the plurality of reflection-typeimage-forming means based on wavelength and emitting the optical imagesincident from the plurality of reflection-type image-forming means so asto run in reverse along the optical axis of the illumination light, aprojection optical system for projecting the optical images, and apolarization beam splitter for emitting the illumination light emittedfrom the light source toward the dichroic prism and emitting apredetermined polarization component in the optical images incident fromthe dichroic prism to the projection optical system, the polarizationbeam splitter and/or the dichroic prism being formed by a membersatisfying the following relationship:${5.00 \times 10^{2}} \geq {{K \cdot \alpha \cdot E \cdot \frac{Cp}{\rho}}{\int_{\lambda_{2}}^{\lambda_{1}}{\left( {1 - T} \right){\lambda}}}}$

where, K: photoelasticity constant of the member (nm/mm·mm²/N),

α: linear expansion coefficient of the member (10⁻⁶/K),

E: Young's modulus of the member (10³N/mm²),

λ: wavelength of the illumination light (nm),

T: internal transmittance of the member at the wavelength λ,

ρ: specific gravity of the member (g/cm³), and

Cp: specific heat of the member (J/g·k),

the integration range in Equation being a range of the light absorptionwavelength band of the member.

Preferably, the light absorption wavelength band is a range of 420 nm to500 nm.

Alternatively, preferably, a polarization separation element forselectively transmitting illumination light of a plane polarizationcorresponding to the plane polarization of the light incident on thereflection-type image-forming means and selectively reflecting thecomponent of the plane polarization orthogonal to that planepolarization is arranged between the light source and the polarizationbeam splitter.

Preferably, the polarization separation element is formed on an incidentfacet of the illumination light of the polarization beam splitter.

Alternatively, preferably, a polarization separation element forselectively transmitting incident light of a predetermined planepolarization corresponding to the plane polarization of the opticalimage and selectively reflecting the component of the plane polarizationorthogonal to that plane polarization is arranged between the projectionoptical system and the polarization beam splitter.

Preferably, the polarization separation element is formed on an emissionfacet of the optical image of the polarization beam splitter.

According to the present invention, if the inclination of the wavelengthseparation mirror is set so that the angle exhibited by the optical axisof the incident light on the wavelength separation mirror and theoptical axis of the first optical image becomes smaller than 90 degrees,it is possible to reduce the difference of the wavelengths in thep-polarization component and the s-polarization component reflected atthe wavelength separation mirror. Accordingly, a high quality image canbe displayed by improving the efficiency of utilization of theillumination light by that amount.

Further, if the inclination of the first wavelength separation mirror isset so that the angle exhibited by the optical axis of the incidentlight on the first wavelength separation mirror and the optical axis ofthe first optical image becomes smaller than 90 degrees and, further, ifthe inclination of the second wavelength separation mirror is set sothat the angle exhibited by the optical axis of the light incident onthe second wavelength separation mirror and transmitted through thefirst wavelength separation mirror and the optical axis of the secondoptical image becomes smaller than 90 degrees, the difference ofwavelengths in the p-polarization component and the s-polarizationcomponent of the reflected light can be reduced in wavelength separationmirrors having a so-called three-plate type structure and, accordingly,a high quality image can be displayed by improving the efficiency ofutilization of the illumination light by that amount.

If a polarization separation element is arranged between the lightsource and the light separating means, the component never modulated bythe reflection-type image forming means is blocked and this componentcan be returned to the light source side. By this, a lowering of thecontrast due to the projection of this component is prevented, and thusthe high quality image can be displayed. Further, the efficiency ofutilization of the illumination light can be improved by utilizing thiscomponent again, and a temperature rise can be prevented by that amount.

Further, if a polarization separation element is arranged between theprojection optical system and the light separating means, the componentlowering the contrast in the projected image is blocked and thiscomponent can be returned to the light source side. By this, thelowering of the contrast due to the projection of this component isprevented and a high quality image can be displayed. Further, theefficiency of utilization of the illumination light can be improved byutilizing this component again, and a temperature rise can be preventedby that amount.

Further, according to the present invention, even if the birefringenceis increased in a member satisfying the relationships due to an increaseof stress by the rise of the temperature, the degree of thebirefringence can be made to stay in a range enough for the practicaluse. By this, the above haze phenomenon due to the birefringence can bereduced and it becomes possible to improve the contrast by that amountand display a high quality display image.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become clearerfrom the following description of the preferred embodiments given withreference to the accompanying drawings, in which:

FIG. 1 is a view of the configuration of a projection-type displaydevice of the related art,

FIG. 2 is a view of the configuration of a first embodiment of aprojection-type display device according to the present invention,

FIG. 3 is a graph of the characteristics of a dichroic mirror,

FIG. 4 is a view of the configuration of a second embodiment of aprojection-type display device according to the present invention,

FIG. 5 is a view for explaining a function of a polarization separationelement of FIG. 4,

FIG. 6 is a view of the configuration of a third embodiment of aprojection-type display device according to the present invention,

FIG. 7 is a view of the configuration of a fourth embodiment of aprojection-type display device according to the present invention,

FIG. 8 is a view of the configuration of a fifth embodiment of aprojection-type display device according to the present invention,

FIG. 9 is a graph for explaining the operation of the projection-typedisplay device of FIG. 8,

FIG. 10 is a view of the configuration of a sixth embodiment of aprojection-type display device according to the present invention,

FIG. 11 is a view of the configuration of a seventh embodiment of aprojection-type display device according to the present invention, and

FIG. 12 is a view of the configuration for explaining the function ofthe polarization separation element of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, embodiments of the present invention will be explained in detailby appropriately referring to the drawings.

FIRST EMBODIMENT

FIG. 2 is a view of the configuration of a first embodiment of aprojection-type display device according to the present invention.

In a projection-type display device 30 of FIG. 2, a light source 31 iscomprised of a xenon lamp 32 arranged in the vicinity of a reflector 33formed by a substantially parabolic mirror and emits the whiteillumination light emitted from the xenon lamp 32 from an opening of thereflector 33.

Further, the light source 31 is provided with a pair of fly eye lenses34A and 34B arranged on the optical path of this illumination light. Dueto this, the distribution of the amount of the illumination light ismade uniform.

Further, the light source 31 is provided with a plane polarizationconversion sheet 35 arranged between these fly eye lenses 34A and 34B.

Here, the plane polarization conversion sheet 35 is an optical elementwhich mainly selectively transmits the s-polarization component, thatis, the polarized light which can be effectively spatially modulated atthe reflection-type liquid crystal panels 36A, 36B, and 36C, in thisprojection-type display device 30 therethrough and convertsp-polarization component orthogonal to this to s-polarization component.

By this, the light source 31 increases the polarization componenteffective for the image display in the illumination light emitted withvarious plane polarizations from the xenon lamp 32, and reduces thepolarization component orthogonal to this and emits the resultantillumination light. As a result, the efficiency of utilization of theillumination light is improved and the contrast of the display image isimproved.

The convex lens 37 converges and emits the illumination light on theoptical path of the illumination light emitted from the fly eye lens34B.

The mirror 38 is struck by the illumination light emitted from thisconvex lens 37 and reflects and emits this in a 90 degree direction withrespect to the path of the incident light.

A convex lens 39 converges and emits the illumination light reflected atthis mirror 38.

A polarization filter 40 selectively transmits the s-polarizationcomponent effective for the image display in the illumination lightemitted from the convex lens 39 therethrough and absorbs thep-polarization component orthogonal to this. By this, the polarizationfilter 40 selectively emits only the s-polarization component effectivefor the image display from the light source side toward a polarizationbeam splitter 41.

The polarization beam splitter 41 selectively reflects an s-polarizationcomponent necessary for the image display, and selectively transmits ap-polarization component orthogonal to this therethrough. By this, thepolarization beam splitter 41 reflects most of the illumination lightincident from the polarization filter 40 and bends the optical path by90 degrees, but, in contrast, selectively transmits the p-polarizationcomponents of the optical images resulting from the p-polarization andthe s-polarization from the reflection-type liquid crystal panels 36A,36B, and 36G running in reverse along this optical path.

The dichroic mirror 42B functions as a wavelength separation mirrorwhich is formed by laminating transparent dielectric films on sheetglass, selectively reflects components having a predetermined wavelengthin the incident light, and selectively transmits the remainingcomponents therethrough. The dichroic mirror 42B selectively reflectsthe illumination light component of the blue band in the illuminationlight emitted from the polarization beam splitter 41, emits this towardthe reflection-type liquid crystal panel 36B, and transmits theremaining components therethrough.

The reflection-type liquid crystal panel 36B is driven by a blue colorsignal and forms the blue image in the image to be displayed by thisprojection-type display device 30. The reflection-type liquid crystalpanel 36B transmits the illumination light incident from the dichroicmirror 42B therethrough, reflects it at a reflection plate arranged atits back surface, and transmits it therethrough again and emits this andthereby emits modulated light with a plane polarization rotatedaccording to the blue image. By this, the reflection-type liquid crystalpanel 36B emits the optical image of the synthesized light of thep-polarized light and the s-polarized light to the dichroic mirror 42Bfor the illumination light incident due to the s-polarization.

The dichroic mirror 42B selectively reflects the modulated lightincident from the reflection-type liquid crystal panel 36B in this wayand emit it to the polarization beam splitter 41 and transmits themodulated light incident from a further continuing dichroic mirror 42Rtherethrough to emit it to the polarization beam splitter 41.

The dichroic mirror 42B is arranged inclined by an angle of 45 degreeswith respect to the optical axis of the incident light so that an angleθ1 exhibited by the optical axis of the incident light and the opticalaxis of the optical image obtained from the reflection-type liquidcrystal panel 36B becomes smaller than 90 degrees.

The dichroic mirror 42B was arranged in this way for the followingreason.

Namely, in the dichroic mirror 42B for selectively reflecting only theincident light having the intended wavelength, the cutoff wavelength forthe selective transmission and reflection is different between thep-polarization component and the s-polarization component which strikeat an angle as shown by the reflectance of the p-polarization componentand the reflectance of the s-polarization component shown by the symbolsRP and RS in FIG. 3. Contrary to this, this type of projection-typedisplay device 30 reflects the incident light of the s-polarizationcomponent for the reflection-type liquid crystal panel 36B, reflects theoptical image of the p-polarization component incident from thisreflection-type liquid crystal panel 36B, and emits it to thepolarization beam splitter 41. Due to this, when the cutoff wavelengthfor selective transmission is different between the p-polarizationcomponent and the s-polarization component in this way, the efficiencyof utilization of the light will be lowered by that amount.

However, there is the characteristic feature that if the incident angleof the incident light becomes smaller, the difference of the cutoffwavelength in reflected lights of the p-polarization component and thes-polarization component is lowered by that amount.

Therefore, the projection-type display device 30 is provided with thedichroic mirror 42B arranged inclined at an angle of 45 degrees withrespect to the optical axis of the incident light so that the angle θ1exhibited by the optical axis of the incident light and the optical axisof the optical image obtained from the reflection-type liquid crystalpanel 36B becomes smaller than 90 degrees.

Further, the reflection-type liquid crystal panel 36B is arranged closeto the polarization beam splitter 41 side so that the shape of theentire projection-type display device 30 can be reduced.

The dichroic mirror 42R functions as a wavelength separation mirrorwhich is formed by laminating transparent dielectric films on sheetglass, selectively reflects the components of predetermined wavelengthsin the incident light, and selectively transmits the remainingcomponents therethrough. The dichroic mirror 42R selectively reflectsthe illumination light component of the red band in the illuminationlight transmitted through the dichroic mirror 42B and emits this towardthe reflection-type liquid crystal panel 36R, while transmits theremaining components and emits them toward the reflection-type liquidcrystal panel 36G.

The reflection-type liquid crystal panel 36R is driven by a red colorsignal and forms the red image in the image to be displayed by thisprojection-type display device 30. The reflection-type liquid crystalpanel 36R transmits the illumination light incident from the dichroicmirror 42R therethrough, then reflects it by the reflection platearranged on its back surface, transmits it again, and emits this andthereby emits modulated light with a plane polarization rotatedaccording to the red image. By this, the reflection-type liquid crystalpanel 36R emits the optical image of the synthesized light of thep-polarized light and the s-polarized light to the dichroic mirror 42Rfor the illumination light incident due to the s-polarization.

The reflection-type liquid crystal panel 36G is driven by a green colorsignal and forms the green image in the image to be displayed by thisprojection-type display device 30. The reflection-type liquid crystalpanel 36G transmits the illumination light incident from the dichroicmirror 42R therethrough, then reflects it by the reflection platearranged on its back surface, transmits it again, and emits this,thereby to emit modulated light with a plane polarization rotatedaccording to the green image. By this, the reflection-type liquidcrystal panel 36G emits the optical image of the synthesized light ofthe p-polarized light and the s-polarized light to the dichroic mirror42R for the illumination light incident due to the s-polarization.

The dichroic mirror 42R selectively reflects the modulated lightincident from the reflection-type liquid crystal panel 36R in this wayand emits this to the dichroic mirror 42B, while transmits the modulatedlight incident from the reflection-type liquid crystal panel 36Gtherethrough and emits this to the dichroic mirror 42B.

In the dichroic mirror 42R synthesizing the green and red modulatedlights and emitting the result in this way as well, if the wavelengthbecomes different between the reflection lights of the p-polarizationcomponent and the s-polarization component and the incident angle of theincident light becomes small, the difference of wavelengths becomessmaller by that amount. For this reason, the dichroic mirror 42R isarranged in parallel to the dichroic mirror 42B and arranged inclined atan angle of 45 degrees with respect to the optical axis of the incidentlight so that the angle θ2 exhibited by the optical axis of the incidentlight and the optical axis of the optical image obtained from thereflection-type liquid crystal panel 36R becomes smaller than 90degrees.

Further, the reflection-type liquid crystal panel 36R is arranged closeto the polarization beam splitter 41 side so that the shape of theprojection-type display device 30 can be made smaller as a whole.

The polarization beam splitter 41 mainly supplies the illumination lightdue to the s-polarization emitted from the light source 31 to thesedichroic mirrors 42B, 42R, etc., and transmits the p-polarizationcomponent in the optical image of the synthesized light of thep-polarized light and the s-polarized light generated by thereflection-type liquid crystal panels 36B, 36R, and 36G as a result ofthis therethrough and emits this toward the screen.

The polarization filter 44 selectively transmits the p-polarizationcomponent therethrough on the optical path of the modulated lightemitted from this polarization beam splitter 41, and selectively absorbsthe s-polarization component. The projection optical system 45 enlargesand projects the transmitted light of this polarization filter 44 on thescreen 46.

Next, an explanation will be made of the operation due to thisconfiguration.

In the projection-type display device 30, the reflection-type liquidcrystal panels 36B, 36R, and 36G are driven by the blue, red, and greencolor signals so that images corresponding to the blue, red, and greencolor signals are formed on the reflection-type liquid crystal panels36B, 36R, and 36G. In the projection-type display device 30, theillumination light emitted from the light source 31 is broken down intothe blue, red, and green wavelengths which are then supplied to thereflection-type liquid crystal panels 36B, 36R, and 36G. Due to this,the plane polarizations of the blue, red, and green illumination lightare rotated by the images corresponding to these blue, red, and greencolor signals to generate optical images. The p-polarization componentsof these optical images are selectively projected onto the screen 36 bythe projection optical system 45 so as to project a color display image.

Namely, the illumination light emitted from the light source 31 is madeto strike the polarization beam splitter 41 via the mirror 38. There,the s-polarization component effective for the formation of the opticalimage is reflected at the reflection-type liquid crystal panels 36B,36R, and 36G and broken down into blue, red, and green illuminationlights by continuing dichroic mirrors 42B and 42R. The blue, red, andgreen illumination lights are polarized and reflected at thereflection-type liquid crystal panels 36B, 36R, and 36G to generateblue, red, and green optical images by the synthesized light of thep-polarized light and the s-polarized light. These optical images strikeupon the polarization beam splitter 41 via the dichroic mirrors 42B and42R. The p-polarization components of these modulated light areselectively transmitted through the polarization beam splitter 41,strike the projection optical system 45, and are projected on the screen46 by this projection optical system 45.

At this time, the illumination light obliquely strikes the dichroicmirrors 42B and 42R at an angle due to the s-polarization, while themodulated light obliquely strikes the dichroic mirrors 42B and 42R assynthesized light of the p-polarized light and the s-polarized light.Contrary to this, since the dichroic mirrors 42B and 42R have differentcharacteristics of reflection with respect to wavelength between thep-polarized light and the s-polarized light, the characteristics ofreflection with respect to the wavelength in the illumination light andthe characteristic of reflection in the modulated light are madedifferent (FIG. 3).

In this embodiment, however, the dichroic mirrors 42B and 42R arearranged inclined so that the angle exhibited by the optical axis of theillumination light with respect to the dichroic mirrors 42B and 42R andthe optical axis of the modulated light incident upon the dichroicmirrors 42B and 42R becomes smaller than 90 degrees, therefore thedifference of the cutoff wavelengths in the reflected light of thep-polarized light and the reflected light of the s-polarized light canbe made smaller. Namely, compared with the blue, red, and greenillumination light emitted from the dichroic mirrors 42B and 42R towardthe reflection-type liquid crystal panels 36B, 36R, and 36G, it becomespossible to emit the modulated lights of the blue, red, and greenp-polarized light corresponding to the illumination light toward theprojection optical system 45 with no waste and therefore possible toimprove the efficiency of utilization of the illumination light by thatamount and form a bright high quality display image.

As explained above, the projection-type display device 30 spatiallymodulates the illumination light of the s-polarized light at thereflection-type liquid crystal panels 36B, 36R, and 36G and emits themodulated light of the p-polarized light and the s-polarized light tothe polarization beam splitter 41 via the dichroic mirrors 42B and 42R.

The polarization beam splitter 41 transmits the p-polarization componentin the optical image of the p-polarized light and the s-polarized lightand emits it toward the screen. At this time, the component of theoptical image resulting from the s-polarized light should be separatedfrom the optical image resulting from the p-polarized light at thepolarization beam splitter 41 and not be projected on the screen 46, butpart passes through the polarization beam splitter 41.

If the component of the optical image resulting from the s-polarizedlight is projected on the screen 46, the contrast of the display imagewill be lowered, but in this embodiment, the polarization filter 44 isarranged between the polarization beam splitter 41 and the projectionoptical system 45. Therefore, the s-polarization component transmittingthrough the polarization beam splitter 41 is absorbed bythis-polarization filter 44. Due to this, compared with the related art,the amount of light will be greatly reduced for the s-polarizationcomponent lowering the contrast in this way. Accordingly, the contrastof the display image on the screen 46 is increased by that amount, andit becomes possible to display a high quality display image.

Further, for the illumination light supplied to the reflection-typeliquid crystal panels 36B, 36R, and 36G, while the s-polarizationcomponent in the illumination light supplied from the light source 31 isreflected at the polarization beam splitter 41 and supplied, part of thep-polarization component is reflected and supplied.

If this p-polarization component is reflected without any modulation atthe reflection-type liquid crystal panels 36B, 36R, and 36G andprojected on the screen 46 without any differentiation from the opticalimage (p-polarization component), this component will also lower thecontrast of the display image, but in this embodiment, since thepolarization filter 40 is arranged between the light source 31 and thepolarization beam splitter 41, the p-polarization component is absorbedby this polarization filter 40. Due to this, the amount of light of theillumination light due to the p-polarization supplied to thereflection-type liquid crystal panels 36B, 36R, and 36G is greatlyreduced. Accordingly, the contrast of the display image is increased bythat amount and it becomes possible to display a high quality displayimage.

Further, a uniform amount of the illumination light can be supplied bythe fly eye lenses 34A and 34B arranged at the light source 31, unevenluminance of the display image is prevented by that amount, and itbecomes possible to display a high quality display image also by this.

Further, by the plane polarization conversion sheet 35 arranged betweenthese fly eye lenses 34A and 34B, the p-polarization component which isabsorbed by the polarization filter 40 or passes through thepolarization beam splitter 41 and is never effective for the display ofthe image is partially converted to the s-polarization component andemitted, whereby the efficiency of utilization of the illumination lightis increased by that amount, the luminance level of the display image isimproved, and thereby also it becomes possible to display a high qualitydisplay image. Further, by the lowering of the amount of light of thep-polarization component incident upon the polarization filter 40 inthis way by that amount, the temperature rise at the polarization filter40 can be reduced and deterioration of the characteristics due to thetemperature rise can be prevented.

As explained above, according to the first embodiment, the dichroicmirror was arranged inclined so that the angle exhibited by the opticalaxis of the illumination light incident on the dichroic mirror servingas the wavelength separation mirror and the optical axis of themodulated light becomes smaller than 90 degrees, therefore, in theconfiguration for generating modulated light of the p-polarized lightand the s-polarized light from the illumination light of the s-polarizedlight and projecting the same onto the screen, the difference ofwavelengths in the p-polarization component and the s-polarizationcomponent of the reflected light can be reduced, the efficiency ofutilization of the illumination light can be improved by that amount,and as a result a high quality image can be displayed.

Further, by arranging the polarization filters between the light sourceand the polarization beam splitter and between the polarization beamsplitter and the projection optical system and making them absorb thep-polarization component and the s-polarization component, it ispossible to prevent the above haze phenomenon of the display image andbe able to increase the contrast and therefore able to display a higherquality image by that amount.

SECOND EMBODIMENT

FIG. 4 is a view of the configuration of a second embodiment of aprojection-type display device according to the present invention.

The difference of a projection-type display device 50 according to thesecond embodiment from the projection-type display device 30 accordingto the first embodiment explained above resides in that polarizationseparation elements 51 and 52 are arranged in place of the polarizationfilters as shown in FIG. 4.

Note that since this projection-type display device 50 is configured inthe same way as the projection-type display device 30 mentioned aboveexcept that the polarization separation elements 51 and 52 are arrangedin place of the polarization filters, the corresponding configurationsare indicated by same references and overlapping explanations will beomitted.

The polarization separation elements 51 and 52 are formed by laminatingfilms having predetermined thicknesses having optical anisotropy and, asshown in FIG. 5, selectively transmit the incident light having thepredetermined plane polarizations therethrough, while selectivelyreflect the incident light having the plane polarizations orthogonal tothem.

The polarization separation element 51 is arranged between a convex lens39 and the polarization beam splitter 41 and selectively transmits thes-polarization component in the illumination light incident from thelight source 31 therethrough, while selectively reflects thep-polarization component.

The polarization separation element 52 is arranged between theprojection optical system 45 and the polarization beam splitter 41 andselectively transmits the p-polarization component in the incident lightfrom the polarization beam splitter 41 therethrough, while selectivelyreflects the s-polarization component.

By this, the polarization separation elements 51 and 52 improve thecontrast of the display image.

Further, at this time, unlike polarization filters, they do not absorbthe p-polarization component and s-polarization component, but reflectthem, so the temperature rise can be reduced by that amount.

Note that the light returned to the light source 31 side or thepolarization beam splitter 41 in this way changes in its planepolarization due to multiple reflection etc. at the light source 31 etc.and will reach the polarization separation elements 51 and 52 ascomponents which will pass through the polarization separation elements51 and 52. Due to this, this projection-type display device 50 canimprove the luminance level of the display image by utilizing theillumination light efficiently.

Further, the polarization separation elements 51 and 52 are held andadhered to the incident facet and the emission facet of the polarizationbeam splitter 41 by an optical bonding material.

Due to this, the projection-type display device 50 eliminates the airlayer between the polarization separation element 51 and thepolarization beam splitter 41 and the air layer between the polarizationseparation element 52 and the polarization beam splitter 41 andtherefore prevents the loss of light due to these air layers. Further,the projection-type display device 50, compared with the case of use ofpolarization filters absorbing the predetermined polarization component,radiates the heat generated at the polarization separation elements 51and 52 with a good efficiency to reduce the temperature rise.

Note that, in a configuration using polarization filters as well, it canbe considered to adhere the elements to the polarization beam splitter,but the temperature rise in polarization filters is larger than that ofthe polarization separation elements, therefore there is theapprehension that birefringence will occur at the polarization beamsplitter due to the temperature rise of the polarization beam splitterper se, the contrast will be lowered, and further the uniformity will bedeteriorated.

According to the second embodiment, since the polarization separationelement 51 which selectively transmits the s-polarization componenttherethrough, and selectively reflects the p-polarization component isarranged between the light source 31 and the polarization beam splitter41, the contrast of the display image is improved and a high qualitydisplay image can be formed.

Further, since the polarization separation element 52 which selectivelytransmits the p-polarization component therethrough, and selectivelyreflects the s-polarization component is arranged between the projectionoptical system 45 and the polarization beam splitter 41, the contrast ofthe display image is improved and a high quality display image can beformed.

Further, since these polarization separation elements 51 and 52 are heldadhered to the polarization beam splitter 41, the loss of the light dueto the air layer is prevented and thus a bright high quality displayimage can be displayed. Further, since the temperature rise can bereduced, the reliability can be improved by that amount, an aging can beprevented, and further the work required for the arrangement can besimplified.

THIRD EMBODIMENT

FIG. 6 is a view of the configuration of a third embodiment of aprojection-type display device according to the present invention.

In a projection-type display device 60 according to the thirdembodiment, a polarization beam splitter 61 having a differenttransmitting and reflecting plane polarization from that of thepolarization beam splitter 41 of the projection-type display device 50of the second embodiment mentioned above is arranged. The arrangement ofthe optical system is changed corresponding to this.

Note that, in this projection-type display device 60, the sameconfigurations as those of the projection-type display device 50mentioned above are indicated by corresponding references andoverlapping explanations will be omitted.

Namely, in this projection-type display device 60, the polarization beamsplitter 61 transmits the s-polarization component therethrough andreflects the p-polarization component. Corresponding to this, thedichroic mirror 42R etc. are arranged on the optical path of theillumination light transmitted through the polarization beam splitter61.

As shown in FIG. 6, even in the case where a polarization beam splitterof a different configuration is used, similar effects to those by thesecond embodiment can be obtained.

FOURTH EMBODIMENT

FIG. 7 is a view of the configuration of a fourth embodiment of aprojection-type display device according to the present invention.

In this projection-type display device 70, the illumination light isbroken down into red, blue, and green illumination lights by a dichroicprism 72 in place of the dichroic mirrors 42R, 42B in theprojection-type display device 30 and the red, blue, and green opticalimages are synthesized.

As in FIG. 7, even if the illumination light is broken down into red,blue, and green illumination light by a dichroic prism 72 in place ofthe dichroic mirrors 42R, 42B and red, blue, and green optical imagesare combined, similar effects as those by the above embodiment can beobtained.

Note that, in the first to fourth embodiments, the description was madeof the cases where polarization filters or polarization separationelements are arranged on the light source side and projection opticalsystem side of the polarization beam splitter, but the present inventionis not limited to these. It is also possible if they are arranged oneither side in the case where characteristics enough for practical usecan be obtained.

Further, in the third and fourth embodiments, the description was madeof cases where the polarization separation elements were held adhered tothe polarization beam splitter, but the present invention is not limitedto these. It is also possible if they are arranged with an air layerinterposed therebetween in the case where characteristics enough forpractical use can be obtained.

Further, in the third and fourth embodiments, the description was madeof cases where the polarization separation elements were constituted bylaminating films having predetermined thicknesses having opticalanisotropy, but the present invention is not limited to these. It isalso possible if this type of polarization separation element isconstituted by laminating transparent members having optical anisotropyto a predetermined thickness on for example a glass plate.

Further, in the third and fourth embodiments, the description was madeof cases where the polarization separation elements were simplyarranged, but the present invention is not limited to this. It is alsopossible if the polarization separation elements are arranged by ARcoating.

FIFTH EMBODIMENT

FIG. 8 is a view of the configuration of a fifth embodiment of aprojection-type display device according to the present invention.

The difference of a projection-type display device 80 of the fifthembodiment from the projection-type display devices 30, 50, 60, and 70of the first to fourth embodiments resides in that, in place of thearrangement of the polarization filters or polarization separationelements on the light source side and projection optical system side ofthe polarization beam splitter, as will be mentioned later, apolarization beam splitter placing predetermined conditions on thestructural parameters is constituted, whereby the lowering of thecontrast due to the above haze phenomenon is stopped to an extentsufficient for practical use and a high quality image can be displayed.

Below, an explanation will be made of the concrete configuration andoperation of the projection-type display device 80 according to thefifth embodiment in sequence in relation to FIG. 8 and FIG. 9.

In the projection-type display device 80 of FIG. 8, a light source 81 iscomprised of an xenon lamp 82 arranged in the vicinity of a reflector 83formed by a substantially parabolic mirror and emits white illuminationlight from the xenon lamp 82 from an opening of the reflector 83.

Further, the light source 81 is provided with a pair of fly eye lenses84A and 84B arranged on the optical path of this illumination light soas to make the distribution of the amount of the illumination lightuniform.

Further, the light source 81 is provided with a plane polarizationconversion sheet 85 arranged between these fly eye lenses 84A and 84B.

Here, the plane polarization conversion sheet 85 is an optical elementwhich mainly selectively transmits the s-polarization component, thatis, the polarized light which can be effectively spatially modulated atthe reflection-type liquid crystal panels 86A, 86B, and 86C, in thisprojection-type display device 80 therethrough, and convertsp-polarization component orthogonal to this to s-polarization component.

By this, the light source 81 increases the polarization componenteffective for the image display in the illumination light emitted withvarious plane polarizations from the xenon lamp 82, and reduces thepolarization component orthogonal to this and emits the resultantillumination light. As a result, the efficiency of utilization of theillumination light is improved and the contrast of the display image isimproved.

The convex lens 87 converges and emits the illumination light on theoptical path of the illumination light emitted from the fly eye lens84B.

The mirror 88 is struck by the illumination light emitted from thisconvex lens 87 and reflects and emits this in a 90 degree direction withrespect to the path of the incident light.

A convex lens 89 converges and emits the illumination light reflected atthis mirror 88.

A polarization beam splitter 90 selectively reflects the s-polarizationcomponent effective for the image display, and selectively transmits thep-polarization component orthogonal to this therethrough. By this, thepolarization beam splitter 90 reflects most of the illumination lightincident from the convex lens 89 and bends the optical path by 90degrees, but in contrast selectively transmits the p-polarizationcomponent of the optical image of the p-polarization and thes-polarization from the reflection-type liquid crystal panels 86B, 86R,and 86G running in reverse through this optical path.

The polarization beam splitter 90 having such a function is formed byadhering the inclined facets of rectangular prisms to each other.Dielectric films are laminated on the adhered facets to form detectionplanes for detecting the incident light.

In the polarization beam splitter 90, a bottom surface of eachrectangular prism is formed to a length of 50 mm. Due to this, thesplitter is formed overall to a cubic shape of a length of 50 mm to aside.

The polarization beam splitter 90 is configured with the rectangularprisms formed by a glass material having a parameter A indicated by thefollowing equation of a value 3.71×10², whereby the birefringence due tothe thermal stress is reduced: $\begin{matrix}{{A = {{K \cdot \alpha \cdot E \cdot \frac{Cp}{\rho}}{\int_{\lambda_{2}}^{\lambda_{1}}{\left( {1 - T} \right){\lambda}}}}}\quad} & (1)\end{matrix}$

where, K: photoelasticity constant of the glass material (nm/mm·mm²/N),

α: linear expansion coefficient of the glass material (10⁻⁶/K),

E: Young's modulus of the glass material (10³N/mm²),

λ: wavelength of the illumination light (nm),

T: internal transmittance of the glass material at the wavelength λ,

ρ: specific gravity of the glass material (g/cm³), and

Cp: specific heat of the glass material (J/g·k).

The integration range in Equation (1) is a range of the light absorptionwavelength band of the glass material (420 nm(λ1) to 500 nm(λ2)).

The dichroic mirror 91B is formed by laminating transparent dielectricfilms on sheet glass and functions as a wavelength separation mirrorwhich selectively reflects components of predetermined wavelengths inthe incident light, and selectively transmits the remaining componentstherethrough. The dichroic mirror 91B selectively reflects the blue bandillumination light component in the illumination light emitted from thepolarization beam splitter 90, emits this toward the reflection-typeliquid crystal panel 86B, and transmits the remaining componentstherethrough.

The reflection-type liquid crystal panel 86B is driven by a blue colorsignal and forms the blue image in the image to be displayed by thisprojection-type display device 80. The reflection-type liquid crystalpanel 86B transmits the illumination light incident from the dichroicmirror 91B therethrough, then reflects it at a reflector plate arrangedon its back surface, and transmits this therethrough again and emit itand thereby emit the modulated light with a plane polarization rotatedaccording to the blue image. By this, the reflection-type liquid crystalpanel 86B emits an optical image of the synthesized light of thep-polarized light and the s-polarized light to the dichroic mirror 91Bwith respect to illumination light emitted by s-polarization.

The dichroic mirror 91B selectively reflects the modulated lightincident from the reflection-type liquid crystal panel 86B in this wayand emits this to the polarization beam splitter 90, while transmits themodulated light incident from the further continuing dichroic mirror 91Rand emits this to the polarization beam splitter 90.

The dichroic mirror 91B is arranged inclined by an angle of 45 degreeswith respect to the optical axis of the incident light so that the angleθ1 exhibited by the optical axis of the incident light and the opticalaxis of the optical image obtained from the reflection-type liquidcrystal panel 86B becomes smaller than 90 degrees.

The dichroic mirror 91B was arranged in this way for the followingreason.

Namely, in the dichroic mirror 91B for selectively reflecting only theincident light having the intended wavelength, the cutoff wavelength forthe selective transmission and reflection is different between thep-polarization component and the s-polarization component which strikeat an angle. Contrary to this, this type of projection-type displaydevice 80 reflects the incident light of the s-polarization componentfor the reflection-type liquid crystal panel 86B, reflects the opticalimage of the p-polarization component incident from this reflection-typeliquid crystal panel 86B, and emits it to the polarization beam splitter90. Due to this, when the cutoff wavelength for selective transmissionis different between the p-polarization component and the s-polarizationcomponent in this way, the efficiency of utilization of the light willbe lowered by that amount.

However, there is the characteristic feature that if the incident angleof the incident light becomes smaller, the difference of the cutoffwavelength in reflected lights of the p-polarization component and thes-polarization component is lowered by that amount.

Therefore, the projection-type display device 80 is provided with thedichroic mirror 91B arranged inclined at an angle of 45 degrees withrespect to the optical axis of the incident light so that the angle θ1exhibited by the optical axis of the incident light and the optical axisof the optical image obtained from the reflection-type liquid crystalpanel 86B becomes smaller than 90 degrees.

Further, the reflection-type liquid crystal panel 86B is arranged closeto the polarization beam splitter 90 side so that the shape of theentire projection-type display device 80 can be reduced.

The dichroic mirror 91R functions as a wavelength separation mirrorwhich is formed by laminating transparent dielectric films on sheetglass, selectively reflects the components of predetermined wavelengthsin the incident light, and selectively transmits the remainingcomponents therethrough. The dichroic mirror 91R selectively reflectsthe illumination light component of the red band in the illuminationlight transmitted through the dichroic mirror 91B and emits this towardthe reflection-type liquid crystal panel 86R, while transmits theremaining components and emits them toward the reflection-type liquidcrystal panel 86G.

The reflection-type liquid crystal panel 86R is driven by a red colorsignal and forms the red image in the image to be displayed by thisprojection-type display device 80. The reflection-type liquid crystalpanel 86R transmits the illumination light incident from the dichroicmirror 91R therethrough, then reflects it by the reflection platearranged on its back surface, transmits it again, and emit this andthereby emits modulated light with a plane polarization rotatedaccording to the red image. By this, the reflection-type liquid crystalpanel 86R emits the optical image of the synthesized light of thep-polarized light and the s-polarized light to the dichroic mirror 91Rfor the illumination light incident due to the s-polarization.

The reflection-type liquid crystal panel 86G is driven by a green colorsignal and forms the green image in the image to be displayed by thisprojection-type display device 80. The reflection-type liquid crystalpanel 86G transmits the illumination light incident from the dichroicmirror 91R therethrough, then reflects it by the reflection platearranged on its back surface, transmits it again, and emits this,thereby to emit modulated light with a plane polarization rotatedaccording to the green image. By this, the reflection-type liquidcrystal panel 86G emits the optical image of the synthesized light ofthe p-polarized light and the s-polarized light to the dichroic mirror91R for the illumination light incident due to the s-polarization.

The dichroic mirror 91R selectively reflects the modulated lightincident from the reflection-type liquid crystal panel 86R in this wayand emits this to the dichroic mirror 91B, while transmits the modulatedlight incident from the reflection-type liquid crystal panel 86Gtherethrough and emits this to the dichroic mirror 91B.

In the dichroic mirror 91R synthesizing the green and red modulatedlights and emitting the result in this way as well, if the wavelengthbecomes different between the reflection lights of the p-polarizationcomponent and the s-polarization component and the incident angle of theincident light becomes small, the difference of cutoff wavelengthsbecomes smaller by that amount. For this reason, the dichroic mirror 91Ris arranged in parallel to the dichroic mirror 91B and arranged inclinedat an angle of 45 degrees with respect to the optical axis of theincident light so that the angle θ2 exhibited by the optical axis of theincident light and the optical axis of the optical image obtained fromthe reflection-type liquid crystal panel 86R becomes smaller than 90degrees.

Further, the reflection-type liquid crystal panel 86R is arranged closeto the polarization beam splitter 90 side so that the shape of theprojection-type display device 80 can be made smaller as a whole.

The polarization beam splitter 90 mainly supplies the illumination lightdue to the s-polarization emitted from the light source 81 to thesedichroic mirrors 91B, 91R, etc., and transmits the p-polarizationcomponent in the optical image of the synthesized light of thep-polarized light and the s-polarized light generated by thereflection-type liquid crystal panels 86B, 86R, and 86G as a result ofthis therethrough and emits this toward the screen.

The projection optical system 92 enlarges and projects the transmittedlight of this polarization beam splitter 91 on a screen 93.

Next, an explanation will be made of the operation by the aboveconfiguration.

In the projection-type display device 80, the reflection-type liquidcrystal panels 86B, 86R, and 86G are driven by the blue, red, and greencolor signals and images corresponding to the blue, red, and green colorsignals are formed on the reflection-type liquid crystal panels 86B,86R, and 86G. The projection-type display device 80 breaks down theillumination light emitted from the light source 81 to wavelengths ofblue, red, and green and supplies them to the correspondingreflection-type liquid crystal panels 86B, 86R, and 86G thereby torotate the plane polarizations of the blue, red, and green illuminationlights by images corresponding to the blue, red, and green color signalsand generate the optical images, selectively projects the p-polarizationcomponents in these optical images by the projection optical system 92onto the screen 93, and thus projects a colored display image.

Namely, the illumination light emitted from the light source 81 strikesthe polarization beam splitter 90 via the mirror 88. There, thes-polarization component to be used for the formation of the opticalimage is reflected at the reflection-type liquid crystal panels 86B,86R, and 86G and broken down to the blue, red, and green illuminationlights by the continuing dichroic mirrors 91B and 91R. The blue, red,and green illumination lights are reflected at the reflection-typeliquid crystal panels 86B, 86R, and 86G and blue, red, and green opticalimages of the synthesized light of the p-polarized light and thes-polarized light are generated. These optical images strike thepolarization beam splitter 90 via the dichroic mirrors 91B and 91R. Thep-polarization components of the modulated light selectively passthrough the polarization beam splitter 90, strike the projection opticalsystem 92, and are projected on the screen 93 by this projection opticalsystem 92.

At this time, the illumination light obliquely strike the dichroicmirrors 91B and 91R by the s-polarization, and the modulated lightobliquely strike the dichroic mirrors 91B and 91R as the synthesizedlight of the p-polarized light and the s-polarized light. On the otherhand, the dichroic mirrors 91B and 91R have different characteristics ofreflection with respect to wavelength between the s-polarized light andthe polarized light, so the characteristic of reflection with respect tothe wavelength in the illumination light and the characteristic of thereflection in the modulated light become different.

In this embodiment, however, the dichroic mirrors 91B and 91R arearranged inclined so that the angle exhibited by the optical axis of theillumination light incident on the dichroic mirrors 91B and 91R and theoptical axis of the modulated lights incident upon the dichroic mirrors91B and 91R is made smaller than 90 degrees, therefore the difference ofthe cutoff wavelength between the reflected light of the s-polarizedlight and the reflected light of the p-polarized light can be madesmall. Namely, with respect to the blue, red, and green illuminationlights emitted toward the reflection-type liquid crystal panels 86B,86R, and 86G at the dichroic mirrors 91B and 91R, the modulated light ofthe blue, red, and green p-polarization corresponding to theillumination light can be emitted toward the projection optical system92 with no waste, therefore the efficiency of utilization of theillumination light can be improved by that amount and a bright highquality display image can be formed.

As mentioned above, in the projection-type display device 80, theillumination light of the s-polarization is spatially modulated at thereflection-type liquid crystal panels 36B, 36R, and 36G and modulatedlight of the p-polarization and the s-polarization are emitted andstrike the polarization beam splitter 90 via the dichroic mirrors 91Band 91R.

In the polarization beam splitter 90, the p-polarization components inthe optical images of the p-polarization and the s-polarization aretransmitted and emitted toward the screen. At this time, originally thes-polarization components of the optical images are separated from theoptical images by the p-polarization at the polarization beam splitter90 and must not to be projected on the screen 93.

However, when an s-polarization component passes through a rectangularprism constituting the polarization beam splitter 90, the planepolarization of the s-polarization component changes due tobirefringence, whereby the component incident by the s-polarization isdetected at the detection facet as the p-polarization component. Bythis, in the projection-type display device 80, part of thes-polarization component will pass through the polarization beamsplitter 90 and be projected on the screen 93, so the contrast of thedisplay image will be lowered by that amount.

Further, in the illumination light emitted from the light source 81, thep-polarization component is emitted toward the reflection-type liquidcrystal panels 86B, 86R, and 86G by the detection at the detection facetof the polarization beam splitter 90, but at this time, due to thebirefringence of the rectangular prisms constituting the polarizationbeam splitter 90, the s-polarization component is mixed into thep-polarization component and emitted. This s-polarization component willbe reflected at the reflection-type liquid crystal panels 86B, 86R, and86G and then pass through the polarization beam splitter 90 and beprojected on the screen 93. Thus the contrast of the display image willbe lowered by that amount.

In this embodiment, however, since the rectangular prisms are formed bya glass material having the parameter A indicated by Equation (1) withthe value 3.71×10², the p-polarization component and the s-polarizationcomponent increasing due to the birefringence can be stopped in a rangeenough for practical use, and the lowering of the contrast due to theabove haze phenomenon is prevented by that amount.

Namely, if the degree of the birefringence can be reduced in therectangular prisms constituting the polarization beam splitter 90 fromcauses of the above haze phenomenon, the phenomenon can be reduced bythat amount. This birefringence occurs due to the stress inside theglass material and can be determined by the value of the optical pathlength×optical elastic constant×stress indicating the amount of strainof the glass material as a yardstick.

Of these, the optical elastic constant has a constant value dependentupon the glass material, therefore it has been considered that this typeof haze phenomenon can be reduced by managing this optical elasticconstant. However, even if the optical elastic constant is greatlyreduced, if it is a glass material having a large stress, it becomesdifficult to reduce the birefringence by that amount.

Therefore, when investigating the stress, in this type of glassmaterial, the stress is represented by thermal stress+initialstress+attachment stress. Here, the thermal stress is the stress ofdisplacement according to the temperature rise of the glass material. Inthe projection-type display device 80, it occurs due to a temperaturerise due to thermal convection inside the set, heat conductivity, lossof illumination light, or the like. Further, the initial stress is aresidual stress from the time of fabrication of the polarization beamsplitter 90 and is generated due to the residual stress when the glassmaterial becomes hard, the residual stress at the cutting and polishingof the glass material, the residual stress due to the heat when formingthe detection facet, the shrinkage of the bonding material at adhesion,and so on. Further, the attachment stress is a stress that is added tothe polarization beam splitter 90 when the polarization beam splitter 90is arranged.

When the power of the projection-type display device 80 is turned on ina state where the internal temperature is sufficiently low and thedisplay image is observed, it was learned that, immediately after thepower was turned on, as shown in FIG. 9, the above haze phenomenon couldbe prevented to an extent enough for practical use, but in contrast, theabove haze phenomenon increased along with the elapse of time. Thisindicates that the stress having the biggest influence upon thebirefringence in the stress represented by thermal stress+initialstress+attachment stress in this way is the thermal stress and that ifthe amount of strain due to this thermal stress is managed, the hazephenomenon can be sufficiently reduced.

By this, when further considering this thermal stress, it is possible torepresent the thermal stress by physical constants defining thecharacteristics of this type of glass material and to thereby representit by the temperature difference×linear expansion coefficient×Young'smodules. Further, the temperature difference can be represented by thespecific heat, specific gravity, and transmittance.

When considering this, the degree of the above haze phenomenon due tothe birefringence can be judged by the parameter A by Equation (1).

In actuality, when investigating this comparing the polarization beamsplitter 90 made by a glass material having a parameter A with a valueof 3.71×10² according to this embodiment and a polarization beamsplitter made by a glass material having a parameter A with a value of5.44×10², as shown in FIG. 9, in the one having a parameter A with avalue of 5.44×10², the above haze phenomenon increased for a few hoursand a reduction of the contrast was perceived due to the phenomenon.Contrary to this, in the one having a parameter A with a value of3.71×10², even if it was used for a long time, it was difficult to see areduction of the contrast due to the haze phenomenon, so it was seenthat a high quality image could be sufficiently displayed for practicaluse.

When judging these evaluation results overall, in order to stop thereduction of the contrast due to the birefringence of the polarizationbeam splitter to a range enough for practical use, in actuality, if aglass material having a parameter A with a value of 5.00×10² or less isused, a projection-type display device with a little deterioration ofcontrast and uniformity can be obtained.

In this way, in the projection-type display device 80, the reduction ofthe contrast is prevented, the illumination light can be supplied in anuniform amount by the fly eye lenses 84A and 84B arranged in the lightsource 81, and the unevenness of luminance of the display image can beprevented by that amount. Due to this, it becomes possible to display ahigh quality display image due to this as well.

Further, due to the plane polarization conversion sheet 85 arrangedbetween these fly eye lenses 84A and 84B, the p-polarization componentwhich passes through the polarization beam splitter 90 and is never usedfor the display of the image is partially converted to a s-polarizationcomponent and emitted, whereby the efficiency of utilization of theillumination light is increased by that amount, and the luminance levelof the display image is improved. Due to this as well, it becomespossible to display a high quality display image.

As explained above, according to the fifth embodiment, since thepolarization beam splitter is prepared by using a glass material havinga parameter A indicating the degree of the birefringence due to thethermal stress shown by Equation (1) with a value of 3.71×10², which isa value lower than 5.00×10², the reduction of the contrast due to theabove haze phenomenon can be stopped to an extent enough for practicaluse. Due to this, a high quality display image can be displayed.

Particularly, since the change of the contrast due to heat is small,even if it is turned on for a long time, it becomes possible to obtain astable contrast and uniformity. Further, the thermal stresscharacteristic of the material with respect to an increase of the amountof light accompanying an increase of the luminance of the display imageis improved, whereby it becomes easy to increase the luminance.

Further, according to the fifth embodiment, since the dichroic mirrorwas arranged inclined so that the angle exhibited by the optical axis ofthe illumination light incident on the dichroic mirror serving as thewavelength separation mirror and the optical axis of the modulated lightbecomes an angle smaller than 90 degrees, it becomes possible to reducethe difference of the wavelength in the p-polarization component and thes-polarization component of the reflected light in a configuration forgenerating modulated light of p-polarization and s-polarization fromillumination light of s-polarization and projecting the same on ascreen, the efficiency of utilization of the illumination light can beimproved by that amount, and, as a result, a high quality image can bedisplayed.

SIXTH EMBODIMENT

FIG. 10 is a view of the configuration of a sixth embodiment of aprojection-type display device according to the present invention.

In this projection-type display device 100, in place of the dichroicmirrors 91B and 91R in the projection-type display device 80, theillumination light is broken down into blue, red, and green illuminationlight by the dichroic prism 101 and blue, red, and green optical imagesare synthesized.

Further, in the projection-type display device 100, in addition to thepolarization beam splitter 90, this dichroic prism 10 is prepared byusing a glass material having a parameter A indicated by Equation (1)with a value of 3.71×10².

As shown in FIG. 10, even if the dichroic prism 101 is formed by using aglass material having a parameter A indicating the degree of thebirefringence due to the thermal stress with a value of 3.71×10² similareffects as those by the fifth embodiment can be obtained.

SEVENTH EMBODIMENT

FIG. 11 is a view of the configuration of a seventh embodiment of aprojection-type display device according to the present invention.

In a projection-type display device 110 according to the seventhembodiment, a polarization beam splitter 111 having differenttransmitting and reflecting plane polarizations from those of thepolarization beam splitter 90 of the projection-type display device 80of the fifth embodiment is arranged and the arrangement of the opticalsystem is changed corresponding to this.

Note that, in this projection-type display device 110, the sameconfigurations as those of the projection-type display device 80 areindicated by corresponding references and overlapping explanations willbe omitted.

Namely, in this projection-type display device 110, the polarizationbeam splitter 111 is prepared by using a glass material having aparameter A indicating the degree of the birefringence due to thethermal stress with a value of 3.71×10², transmits the s-polarized beamtherethrough, and reflects the p-polarized light. Corresponding to this,the dichroic mirror 91B etc. are arranged on the optical path of theillumination light passing through the polarization beam splitter 111.

Further, in this projection-type display device 110, polarizationseparation elements 112 and 113 are arranged on the light source sideand the projection optical system side of the polarization beam splitter111.

The polarization separation elements 112 and 113 are formed bylaminating films of predetermined thicknesses having optical anisotropyand selectively transmit the incident light of predetermined planepolarizations shown in FIG. 12 therethrough, while selectively reflectincident light having plane polarizations orthogonal to this.

The polarization separation element 112 is arranged between the convexlens 89 and the polarization beam splitter 111, selectively transmitsthe s-polarization component in the illumination light incident from thelight source 81 therethrough, while selectively reflects thep-polarization component.

The polarization separation element 113 is arranged between theprojection optical system 92 and the polarization beam splitter 111,selectively transmits the p-polarization component in the incident lightfrom the polarization beam splitter 111 therethrough, while selectivelyreflects the s-polarization component.

Due to this, the polarization separation elements 112 and 113 reflectthe components of the plane polarization which become the cause of theabove haze phenomenon to the light source side and can utilize themagain and improve the contrast of the display image and, at the sametime, efficiently utilize the illumination light and improve theluminance level of the display image.

Further, the polarization separation elements 112 and 113 are heldadhered to the incident facet and the emission facet of the polarizationbeam splitter 111.

By this, the projection-type display device 110 eliminates the air layerbetween the polarization separation element 112 and the polarizationbeam splitter 111 and the air layer between the polarization separationelement 113 and the polarization beam splitter 111 and prevents the lossof the light due to these air layers.

Further, the projection-type display device 110 efficiently radiates theheat generated at the polarization separation elements 112 and 113 andreduces the temperature rise.

According to the seventh embodiment, in addition to the configurationaccording to the fifth embodiment, since the polarization separationelements 112 and 113 are arranged between the light source 81 and thepolarization beam splitter 111 and between the projection optical system92 and the polarization beam splitter 111, the above haze phenomenon canbe further prevented. Due to this, the contrast is improved and a highquality display image can be formed.

Further, since these polarization separation elements 112 and 113 areheld adhered to the polarization beam splitter 111, the loss of thelight due to the air layers is prevented, thus a bright high qualitydisplay image can be displayed. Further, the temperature rise can bereduced, therefore the reliability can be improved by that amount, agingcan be prevented, and further the work required for the arrangement canbe simplified.

Note that, in the embodiments, cases where the present invention wasapplied to a projection-type display device using one polarization beamsplitter were explained, but the present invention is not limited tothis and can be widely applied also to the case of allocating apolarization beam splitter for every color and other cases.

While the invention has been described with reference to specificembodiment chosen for purpose of illustration, it should be apparentthat numerous modification could be made thereto by those skilled in theart without departing from the basic concept and scope of the invention.

What is claimed is:
 1. A projection-type display device, comprising: areflection-type image-forming means for spatially modulating andreflecting illumination light of a predetermined plane polarization toemit an optical image with a plane polarization rotated with respect tothe plane polarization of the illumination light; a projection opticalsystem for projecting the optical image; a light source for emittinglight including the illumination light; and a plane polarizationconversion means for converting the emitted light from the light sourceto illumination light of a plane polarization corresponding to the planepolarization of the light incident on the reflection-type image-formingmeans; a polarization beam splitter for emitting the illumination lightdirected from the light source through the plane polarization conversionmeans toward the reflection-type image-forming means in line with anaxis and emitting the optical image redirected from the reflection-typeimage-forming means in line with the axis to the projection opticalsystem; and a polarization separation element forming a plate on anincident facet of the illumination light of the polarization beamsplitter for selectively transmitting illumination light of a planepolarization corresponding to the plane polarization of the lightincident on the reflection-type image-forming means and selectivelyreflecting the component of the plane polarization orthogonal to thatplane polarization arranged between the light source and thepolarization beam splitter.
 2. A projection-type display device,comprising: a reflection-type image-forming means for spatiallymodulating and reflecting illumination light of a predetermined planepolarization to emit an optical image with a plane polarization rotatedwith respect to the plane polarization of the illumination light; aprojection optical system for projecting the optical image; a lightsource for emitting light including the illumination light; a planepolarization conversion means for converting the emitted light from thelight source to illumination light of a plane polarization correspondingto the plane polarization of the light incident on the reflection-typeimage-forming means; a polarization beam splitter for emitting theillumination light directed from the light source through the planepolarization conversion means toward the reflection-type image- formingmeans in line with an axis and emitting the optical image redirectedfrom the reflection-type image-forming means in line with the axis tothe projection optical system; and a polarization separation elementforming a plate on an emission facet of the optical image of thepolarization beam splitter for selectively transmitting incident lightof a plane polarization corresponding to the plane polarization of theoptical image and selectively reflecting the component of the planepolarization orthogonal to that plane polarization arranged between theprojection optical system and the polarization beam splitter.
 3. Aprojection-type display device, comprising: a reflection-typeimage-forming means for spatially modulating and reflecting illuminationlight of a predetermined plane polarization to emit an optical imagewith a plane polarization rotated with respect to the plane polarizationof the illumination light; a projection optical system for projectingthe optical image; a light source for emitting light including theillumination light; a plane polarization conversion means for convertingthe emitted light from the light source to illumination light of a planepolarization corresponding to the plane polarization of the lightincident on the reflection-type image-forming means; a polarization beamsplitter for emitting the illumination light directed from the lightsource through the plane polarization conversion means toward thereflection-type image-forming means in line with an axis and emittingthe optical image redirected from the reflection-type image-formingmeans in line with the axis to the projection optical system; and apolarization separation element forming a plate on an emission facet ofthe optical image of the polarization beam splitter for selectivelytransmitting incident light of a plane polarization corresponding to theplane polarization of the optical image and selectively reflecting thecomponent of the plane polarization orthogonal to that planepolarization arranged between the projection optical system and thepolarization beam splitter.
 4. A projection-type display device as setforth in claim 3, wherein said second polarization separation element isformed on an emission facet of the optical image of said lightseparating means.
 5. A projection-type display device as set forth inclaim 3, wherein said first polarization separation element is formed onan incident facet of the illumination light of said light separatingmeans; and said second polarization separation element is formed on anemission facet of the optical image of said light separating means.
 6. Aprojection-type display device, comprising: a reflection-typeimage-forming means for spatially modulating and reflecting illuminationlight of a predetermined plane polarization to emit an optical imagewith a plane polarization rotated with respect to the plane polarizationof the illumination light; a projection optical system for projectingthe optical image; a light source for emitting light including theillumination light; a polarization beam splitter for emitting theillumination light from the light source toward the reflection-typeimage-forming means and emitting the optical image from thereflection-type image-forming means to the projection optical system;and said polarization beam splitter being formed by a member satisfyingthe following relationship: wherein:${A = {{K \cdot \alpha \cdot E \cdot \frac{Cp}{\rho}}{\int_{\lambda_{2}}^{\lambda_{1}}{\left( {1 - T} \right){\lambda}}}}}\quad$

 A=3.71×10² K: photoelasticity constant of said member (nm/mm·mm²/N), α:linear expansion coefficient of said member (10⁻⁶/K), E: Young's modulusof said member (10³N/mm²), X: wavelength of the illumination light (nm),T: internal transmittance of said member at the wavelength λ, ρ:specific gravity of said member (g/cm³), and Cp: specific heat of saidmember J/g·k), the integration range in Equation being a range of thelight absorption wavelength band of the member.
 7. A projection-typedisplay device as set forth in claim 6, further comprising at least oneof a polarization separation element and a plane polarization conversionmeans between the polarization beam splitter and the light source, saidpolarization separation means selectively transmitting illuminationlight of a plane polarization corresponding to the plane polarization ofthe light incident on the reflection-type image-forming means, saidplane polarization conversion means converting the emitted light fromthe light source to illumination light of a plane polarizationcorresponding to the plane polarization of the light incident on thereflection-type image-forming means.